I would like to try sending data over the traffic channel (voice channel)
on a CDMA phone. Since CDMA has a variable rate voice coder I am assuming that any high speed modulation schemes would be foiled by the vocoder.

My data requirements are pretty small so I am guessing that even with the vocoders I should be able to do AFSK modulation (Bell 103) scheme and the vocoders would allow that to pass thru?

I am planning on trying this out on my Verizon phone but if someone has already tried this it would save me some time :-)

>
>
> My data requirements are pretty small so I am guessing that even with the
> vocoders I should be able to do AFSK modulation (Bell 103) scheme and the
> vocoders would allow that to pass thru?

you were right to worry about phase problems, but there's an even more
insidious problem.. Silences. When the packets don't make it, the phone
fakes it with silence.
Transparent to the ear, but the modem will not be happy. If it works, it's
cause you got lucky.

On 2/1/06, Jay Shroff <spam_OUTjshroffTakeThisOuTmyrealbox.com> wrote:
>
>
> Ahh, you are correct I forgot about that. know of an encoding scheme that
> might work for low data rates over a lossy channel such as CDMA.

All depends on the rate and size of the dropouts.
I've seen ones that dtmf woudn't work through..

From: "Jay Shroff" <.....jshroffKILLspam@spam@myrealbox.com>
> Ahh, you are correct I forgot about that. know of an encoding scheme that
> might work for low data rates over a lossy channel such as CDMA.
> I could compensate for the drop outs by implementing a TCP/IP type
> protocol on top of the encoding layer.
> If only I had a way of turning off the vocoders :-)
> I could live with data rates of 150 - 300 Bps
>

DTMF could probably give you about 20 symbols per second at four bits per
symbol = 80 bits per second. The vocoders have to be tuned to let DTMF
through for obvious reasons.

> On 2/1/06, Jay Shroff <jshroffKILLspammyrealbox.com> wrote:
>>
>>
>> Ahh, you are correct I forgot about that. know of an encoding scheme that
>> might work for low data rates over a lossy channel such as CDMA.
>
>
> All depends on the rate and size of the dropouts.
> I've seen ones that dtmf woudn't work through..

>
> DTMF is sort of guaranteed to pass. You could slow down in case of
> trouble.

You could, but if the silences are punching holes in your tones, it may not
matter how long you keep them on.. You need 50mS of good tone to meet spec,
and usually about 45mS actual minimum for the detector. Get a silence, and
you have to start aaaaalll over, as a film loader!

Thanks Bob & Peter. I guess I will have to go with DTMF. I was hoping that I could do something better. I was told there was a company out there that offered a modulation scheme that could do 800bps over CDMA, but looks like that must be a "marketing spec"

Ironically I am looking to do the same thing over CB radio for very
limited use (unencrypted and all that jazz)
I found this website that you might be interested in. I'm thinking
something could be done very similarly with a few opamps and PLLs. The
XR2206 and 2211 chips don't seem to be easy to find and/or cheap. I
think something like 1200/2200 FSK should be reliable, though I have to
admit I don't know the intricacies of expecting cell phones to work
worth a crap for analog transmission.
I know I do a lot of "what.. What.. WHAT?" on my cell phone.
--
Martin Klingensmith

>Hi All,
>
>I am hoping that someone on piclist has experience with this
>
>I would like to try sending data over the traffic channel (voice channel)
>on a CDMA phone. Since CDMA has a variable rate voice coder I am assuming that any high speed modulation schemes would be foiled by the vocoder.
>
>My data requirements are pretty small so I am guessing that even with the vocoders I should be able to do AFSK modulation (Bell 103) scheme and the vocoders would allow that to pass thru?
>
>I am planning on trying this out on my Verizon phone but if someone has already tried this it would save me some time :-)
>
>Thanks
>Jay
>
>
>
>
>
>

> On 2/6/06, Martin K <@spam@martin-distlistsKILLspamnnytech.net> wrote:
> >
> > Ironically I am looking to do the same thing over CB radio for very
> > limited use (unencrypted and all that jazz)
>
>
> Legalities aside.. Ever hear of a ham radio TNC?
> It's been done.
>
> KPC-3, TNC-2, and several PIC and AVR based versions.
> --

>On 2/6/06, Martin K <KILLspammartin-distlistsKILLspamnnytech.net> wrote:
>
>
>>Ironically I am looking to do the same thing over CB radio for very
>>limited use (unencrypted and all that jazz)
>>
>>
>
>
>Legalities aside.. Ever hear of a ham radio TNC?
>It's been done.
>
>KPC-3, TNC-2, and several PIC and AVR based versions.
>
>
Yes I know what it is. This would just be for one day use for something
like a soap-box derby on steroids. (start/stop signal transmission)
I'm not sure a PIC would be the easiest plan for the analog section, but
for the digital part of course.

Other than that, I suppose I am wondering if I could get a modern modem
to emulate Bell 103 mode?
--
Martin K